1. Field of the Invention
This invention relates to the field of nondestructive testing and particularly to electromagnetic transducers for generating and receiving ultrasonic waves used in ultrasonic inspection of metal parts.
2. Description of the Prior Art
Ultrasonic waves can be generated in conductive materials such as metals by a Lorentz force mechanism using an electromagnetic transducer (EMAT). Such EMAT transducer has a coil which is placed adjacent the surface of the metal and an RF current is fed through the coil. The current in the coil induces eddy currents in the metal which react against an applied static magnetic field to produce the forces that launch the ultrasonic waves.
Recently, a new type of electromagnet transducer has been developed which uses a row of permanent magnets to create a static periodic magnetic field in the material. This periodic magnet EMAT is described in U.S. Pat. Application Ser. No. 830,269, filed Sept. 2, 1977, now U.S. Pat. No. 4,127,035 by Carmine F. Vasile, the inventor of the present unidirectional transducer. When such transducer is used to launch ultrasonic waves parallel to the surface of a metal, at least two waves traveling in opposite directions are generated in the metal. These two waves and their reflections eventually arrive at the receiver and must be identified to interpret the results. This complicates the interpretation of the data and increases the possibility of error.
Further, such prior art multidirectional transducer is less efficient because it emits and receives energy in directions which are not usable, rather than in only a single usable direction.